1. Keep sensor as reasonably clean as possible.
2. Remove the bulk of contaminant by carefully blotting/wiping away debris. Be careful not to rub too vigorously as this may cause static charge.
3. Rinse the sensor in warm tap water or distilled water.
4. Prepare a cleaning solution containing a soap and water mixture. Use dishwashing detergent and warm water. Use only soaps that do not contain abrasives or lanolin.
5. Soak the sensor in this solution for up to five minutes and then gently or while soaking, use a soft bristle brush to gently scrub the bulb and reference area of the sensor.
6. Rinse the pH sensor in warm tap water and check/standardize the sensor in buffer solutions.
If the readings in buffers are still out of tolerance:
7. Soak the sensor in 5% to 10% HCI acid solution for a few – less than five – minutes.
CAUTION!
Do not use this procedure if the sensor has been used in a solution containing cyanide as this may produce poisonous cyanide gas.
8. Rinse the sensor in warm tap water and then place the sensor into a mild soap solution for a minute or two to neutralize any remaining acid and let the sensor come to equilibrium.
9. Rinse in warm tap water and check/standardize the sensor in buffer solutions.
Should the above procedures yield results that are within your operational tolerances, the pH sensor is once again suitable for use. However if the above results do not bring the readings of the pH sensor within tolerance, it is time to replace the sensor
DECISION TREE
The decision tree is a quick graphic interpretation of the procedures outlined in the previous text.
About the Author: Fred Kohlmann is a Product Business Manager for Analytical Products with Endress+Hauser. Since 1976, he has been involved in engineering, design service, marketing, and sales of online analytical water quality and process control instrumentation. Kohlmann has taught accredited course work and authored numerous articles relating to pH, ORP and conductivity measurements. Past publications include "What Is pH and How Is It Measured?", a primer on the use of pH instrumentation, and "Electrical Conductivity Measurements" in the "Process/Industrial Instruments and Controls Handbook", Fourth Edition, by McGraw Hill, Douglas M. Considine Editor.
More WaterWorld Current Issue Articles
More WaterWorld Archives Issue Articles